Boolean does not work in Blender 2.8 beta
the problem is that you have overlapping faces on the bottom of your mesh.



in this example i create 2 cubes and try to make a union operation but it doesn't work because the cubes faces overlap when i scale down one cube the union operation works as expected.

good rule of thumb if you work with booleans if you have a problem try to move one mesh until it works.